The Half-Sync/Half-Async pattern decouples synchronous I/O from
asynchronous I/O in a system to simplify concurrent programming effort without
degrading execution efficiency.
Class diagram
Applicability
Use Half-Sync/Half-Async pattern when
a system possesses following characteristics:
the system must perform tasks in response to external events that occur asynchronously, like hardware interrupts in OS
it is inefficient to dedicate separate thread of control to perform synchronous I/O for each external source of event
the higher level tasks in the system can be simplified significantly if I/O is performed synchronously.
one or more tasks in a system must run in a single thread of control, while other tasks may benefit from multi-threading.